Google has published a document on the most common mistakes webmasters, developers, designers and site owner make when it comes to creating smartphone enabled web sites.
Here is the abbreviated list but check out the full list in the link above:
- Unplayable videos
- Faulty redirects
- Smartphone-only 404s
- App download interstitials
- Irrelevant cross-linking
- Page speed
Probably the most SEO specific items in the faulty redirects:
- Your desktop site's server is configured to redirect smartphone users to the smartphone site's homepage, regardless of which URL they originally requested, even if the mobile site has the equivalent page to the redirecting desktop page.
- Desktop URLs with dynamically generated content and URL parameters that don't map well to the equivalent mobile URL. For example, if a user is looking for a train timetable on a specific date on the desktop site and gets redirected to the general timetable search page on the smartphone-optimized site instead of the actual search.
We recommend that you configure the redirection correctly if you do have an equivalent smartphone URL so that users end up on the page they were looking for.
- Redirecting some mobile devices but not others. For example, a site may redirect only Android users to the mobile site and not redirect iPhone or Windows Phone users.
Forum discussion at Google+.
